The present invention relates to an amorphous magnetic alloy of Co-Nb-Zr system and, more particularly, to an amorphous magnetic alloy of Co-Nb-Zr system suitable for use as the material of magnetic heads, as well as to a magnetic head made from this alloy.
In recent years, the magnetic recording technique has achieved a remarkable progress owing to the development of magnetic tapes with high coercive force and development of materials for high performance magnetic head for use in combination with such magnetic tape. Particularly, metal powder tape having high coercive force affords remarkable improvement in both the output level and C/N ratio (output-noise ratio) in the high recording density region of recording wavelength between several .mu.m and 1 .mu.m or less, as compared with conventional tapes. This in turn makes it possible to attain a remarkable increase in the recording density particularly in the uses which require high recording density such as VTR.
Conventionally, ferrite has been used as the material of the magnetic heads in VTRs. The magnetic head made of ferrite, however, has a saturation flux density which is about 5,000 gauss at the greatest, so that it cannot provide sufficiently large recording field. Under this circumstance, there is an increasing demand for magnetic heads made of metallic magnetic materials having high saturation flux density, in order to enjoy the advantages of the metal powder tape with high coercive force.
Hitherto, crystalline alloys such as Fe-Al-Si system alloys or Fe-Ni system alloys have been used and, in recent years, amorphous magnetic alloys have been developed to cope with this demand. The crystalline alloys such as Fe-Al-Si system alloys and Fe-Ni system alloys, however, have magneto crystalline anisotropy due to their crystalline nature. In order to obtain excellent magnetic properties suitable to the magnetic heads, particularly high magnetic permeability, it is desirable that the composition of the material approximates the composition which nullifies the magneto-crystalline anisotropy. Insofar as the material is used for magnetic heads, it is also necessary to substantially nullify the magnetostriction constant. These requirements undesirably limit the range of composition usable as the material of the magnetic heads and, hence, make the production difficult due to difficulty in the control of composition.
On the other hand, amorphous magnetic alloy offers various advantages. Namely, the amorphous magnetic alloy, which exhibits no magneto-crystalline anisotropy, can have wide selection of composition because only the magnetostriction constant has to be adjusted. In addition, even if the magnetic permeability is degraded due to induced magnetic anisotropy, the original magnetic permeability can easily be recovered by a suitable heat treatment. Moreover, the amorphous magnetic alloys can possess high saturation flux density and high coercive force which could never be attained by crystalline alloys. Furthermore, the amorphous magnetic alloys suffer from only small eddy current loss due to a high electric resistance. There are two types of amorphous alloys of the kind described: namely, metal-metal system amorphous alloy which does not contain any metalloid element and contains metallic element as the glass former element; and metal-metalloid system amorphous alloy containing metalloid element as the glass former element. The metal-metal system amorphous alloy is more suitable for use as the magnetic head material than the metal-metalloid system amorphous alloy because the former has higher crystallization temperature and higher corrosion and wear resistances than the latter.
Hitherto, these amorphous magnetic alloys have been produced by a splat cooling process, in the form of films having thicknesses ranging between 10 and 50 .mu.m. In recent years, however, a remarkable progress has been made in the field of technique for forming thin films, e.g. sputtering, and it has become possible to produce even an amorphous magnetic alloy of such a composition as could never be produced due to oxidation of the specimen. The current technique for forming thin films permits also an easy lamination of the amorphous alloy films and insulating films such as oxide films. This in turn permits the production of a material having reduced eddy current loss and, hence, suited for use as the material of heads in devices operating at high frequency, e.g. VTRs and computers. The current thin film forming technique is applicable also to the production of composite type magnetic head in which the amorphous magnetic alloy is used only in the portion of the magnetic head around the gap while the other portions are made of ferrite, as well as to thin film magnetic recording head.
Japanese Patent Application Laid-Open Publications Nos. 55-138049, 56-84439 and 57-155339 disclose metal-metal system amorphous magnetic alloys, particularly amorphous magnetic alloys containing Zr as the glass former element which are comparatively easy to produce and which have superior properties.
The present inventors have produced thin film of the above-mentioned amorphous magnetic alloy containing Zr by sputtering method and measured the properties of the product film. As a result, the present inventors have found that the amorphous magnetic alloys of Co-Nb-Zr system having compositions disclosed in the above-mentioned Laid-Open Publications and possessing saturation flux density of about 7.5 kG or greater generally exhibit comparatively large magnetostriction constant and, therefore, are rather unsuitable for use as the material of the magnetic heads.